Insulated-gate bipolar transistors (IGBT) are used, for example, in inverter circuits to regulate inductive loads such as electric machines. In the inverter circuits, the IGBTs are connected in parallel to a free-wheeling diode to allow for a bi-directional current, which becomes necessary if IGBTs are to be applied, for example, in connection with inductive loads. The application of parallel free-wheeling diodes, however, involves numerous disadvantages. For instance, the IGBT housing must be designed so as to accommodate both the IGBT body and the separate free-wheeling diode and the bonding of the two components is complex and costly.
To overcome these disadvantages, reverse conducting IGBTs (so called RC-IGBTs) have become popular, such as those disclosed in U.S. Patent Application Publication No. 2007/0231973A1, in which an IGBT and a free-wheeling diode are monolithically formed as one simple semiconductor component. The p-doped collector zone is locally disrupted by incisions, where n-doped semiconductor material contacts the collector metallization, resulting in a so-called PIN-electrode structure between the emitter structure, the lightly doped drift zone and the p-doped material in the MOS-channel zone.
The conducting state of a conventional free-wheeling diode connected antiparallel to an IGBT does not depend on the conduction state of the IGBT, whereas the intrinsic free-wheeling diode of an RC-IGBT is influenced by the conduction state of the MOS-channel zone of the RC-IGBT. That is, if the RC-IGBT is triggered via its gate electrode during its reverse conduction state, the MOS-channel is conductive. Since the MOS-channel allows for a bi-directional current, electrons in the reverse conduction path may follow an additional current path in case of a triggered gate electrode, in the course of which the forward voltage drop may be substantially increased in the PIN-diode structure as not all of the electrons contribute to the flooding of the PIN-diode, which is undesirable in most cases.
In German Patent Application Publication DE 102009001029A1, a control method and a corresponding circuit structure is disclosed that overcomes the problem described hereinbefore, the control method involving a method for detecting the current direction in an RC-IGBT. One disadvantage of this method may be that at least one (or a plurality of serial) diode(s) of high blocking capability is/are necessary, these diodes being costly and needing a large space within a power electronic arrangement due to the required electric creepage distances.
U.S. patent application Ser. No. 12/943,079 discloses a circuit arrangement and a corresponding control method for overcoming the problem described hereinbefore and for preventing the RC-IGBT from being switched on via its gate electrode while in its reverse conducting state, the control method involving a method for detecting the current direction in an RC-IGBT. This method is based on detecting the charge current transferred through the gate connector of an RC-IGBT if the device is switched passively. A passive switching event occurs, if the RC-IGBT goes from forward blocking into reverse conducting mode, or vice versa, without an active switching event of its dedicated gate drive.
The fact, however, that passive switching events can only take place at the beginning of the dead-time in a half bridge configuration poses a problem. If a passive switching event occurs and the RC-IGBT is therefore prevented from being switched on and a zero crossing of the load current occurs while the RC-IGBT is still switched off, this results in highly distorted current waveforms and makes real zero crossing impossible.
There is a general need to overcome or to at least to mitigate the problems discussed above. There is also a need to provide a circuit arrangement and a corresponding method to detect the zero crossing of the load current and switch on the RC-IGBT if a zero crossing occurs.